During the manufacture of a hard disk drive (HDD) it is necessary to provide a magnetic pattern on each surface of each disk that is used by the servo control system for position and timing feedback. This pattern is known as the servo pattern. The process of writing this servo pattern onto each disk is known as servo writing. Typically the servo writing process is done in a cleanroom environment before the HDD is completely sealed, because during the servo writing process it is necessary to have very accurate position and timing feedback so that the servo pattern can be properly written across the entire surface of each disk in the HDD. The position feedback is typically provided by a special purpose positioner that comes in physical contact with the arms which support the heads on each surface of the HDD. The positioner provides the feedback and the ability to move the heads via the arms with sufficient accuracy. The timing feedback is provided by writing a pattern circumferentially around the disk with a dedicated head known as a clock head. It is inserted over one of the disks in the HDD for this purpose during the servo write process and then removed once the process is complete. The timing feedback has also been provided by writing timing signals with the heads in the HDD equally spaced around the circumference of at least one disk. The timing signals, called timing marks, need to be written each time the position of the heads is changed.
As recognized herein, it would be advantageous to servo-write a HDD without any external position or timing feedback to assist in the servo writing process, to allow the servo write process to be moved outside of the cleanroom after the HDD has been sealed. This provides a great cost advantage because cleanroom space is very expensive. Likewise, the present invention recognizes a need to make the above-discussed process more affordable by using the same electronics that are used on the finished product.
As understood herein, during the process of self-servo writing there are three basic patterns that must be written onto the disk. The first pattern is called a timing mark. Its purpose is to provide the timing or circumferential feedback for the self-servo write process. The second pattern is called the radial pattern. Its purpose is to provide the position or radial feedback for the self-servo write process. The third pattern is called the servo pattern. It is the pattern that will ultimately be used by the servo electronics in the HDD to provide timing and position feedback. The writing of the servo pattern is the main goal of the servo writing process. Both the timing marks and radial patterns are overwritten with customer data during the formatting of the HDD in subsequent processes.
The present critically recognizes that in existing HDD data channels, circuitry exists to recognize a timing mark and measure the time between two of them. The present invention further recognizes that this information can be used to calculate where the next three patterns (radial, servo and timing) should be written on the disk. The time to start the writing of these patterns may be controlled by a write delay that is provided to the data channel from a digital signal processor.
As recognized herein, however, the problem is that there are three patterns that must be written, which would otherwise require the generation of three write delays. Moreover, many types of servo patterns require some fields within the pattern to not be written at all, further complicating the task by requiring the write circuitry to be energized and deenergized repeatedly, a process that entails delays in component warm-up, etc. Therefore, without the present invention the write process must be turned off and started up again in the middle of a write between timing marks, requiring the provision of additional write delays to the channel.
With this in mind, the present invention critically recognizes that in typical HDD electronics the data channel is the primary source of position and timing feedback, and that it possesses sufficient accuracy for the servo writing process.